1. Field of the Invention
This invention is addressed to the processes of structural retrofit of masonry buildings, including masonry of all types and degrees of hardness and consistency, from adobe or other earthen construction to the hard granites, basalts and concretes.
2. Description of Prior Art
The optimization of the Air Extraction core-drilling system design for the processes of structural retrofit use is much different from that of well-drilling or geological systems for open drilling in ground or rock strata. Construction wet drilling of short cores in concrete had been developed from these sources. However, dry, or near-dry drilling of longer cores is essential in many structures and highly desirable in nearly all buildings needing reinforcement. Accuracy and wall protection are emphasized in construction structural applications. Cost is of paramount importance. Removal of cuttings is generally more difficult and critical. Encounters with steel are frequent.
The present patent is a result of further development of the air extraction drilling system and resin grouting technology which were proven to first order in the hardware example of method U.S. Pat. No. 5,497,841 by the same inventor, working with another inventor. The U.S. Pat. No. 5,497,841 patent was entitled xe2x80x9cMethods For Coring A Masonry Wallxe2x80x9d, FIG. 1. The specialized technology to accomplish core placement in a larger percentage of structures, expanding its use and efficiency, is the subject of this follow-on patent.
The entire field of structural retrofit through coring of masonry walls, placing reinforcing elements into the cores and filling the cores with a strong adhesive grout, bonding the reinforcement into the structure, has been referred to by engineers as the xe2x80x9cCenter-Core Methodxe2x80x9d.
The solvent-based resinous grouts are also an important and indispensable part of the Center Core technology. They are substantially better than cementious bonding adhesives which require wetting of surfaces with water for adequate bonding. There is a considerable quality-control problem with water-based and cementious materials in regard to this wetting requirement, especially as to uniform optimal wetting. Also, even the strongest cementious adhesives require additives and plasticizers for good retrofit bonding. The stronger mixtures of cementious grouting materials also are not liquid enough; i.e., do not have low enough viscosity to fill all the small cracks and voids left by masons in the original construction. Further, the water in water-based grouting materials is the solvent, but it does not carry the adhesive well into cracks and voids to form a network of bonding.
Properly-selected resinous grouts, on the other hand, permit use of excess low viscosity resin over that needed to saturate the grouting sand, which will therefore fill all accessible small cracks and voids, fully integrating the structure wherever the resin can run or be drawn through gravity and capillary action. The excess resin will always rapidly migrate through several feet or more of wall, even through and into the smallest cracks, dependent on the formulations and the procedural techniques used in the installation of the grout. The larger voids are readily filled with the resin-sand grouting mixture through gravity pressure. The grout can also be pumped, under pressure.
The setting resins, properly formulated, are substantially superior to cementious grouts in regard to adhesive strength and in the ability to integrate the steel and masonry, to absorb shock and deformation. The grout ductility and impact resistance may readily be adjusted through formulation variables. Thus, the dry core-drilling system, steel or other reinforcement insertion procedures and associated resin grouting system form an optimal retrofit combination. University testing has shown that this combination usually will increase the wall strength to a much greater level, as much as several times that of the wet-drilling and cementious grouting combination. It is usually stronger than the equivalent original reinforcement applied in new construction to current building codes, depending on the size and spacing of the cores.
The structural engineer should evaluate the number of cracks and voids in the wall as well as the mortar strength and other reinforcement parameters, comparing the structural retrofit being designed with that of test data and earthquake experience available for this specialized Center-Core technology. This comparison data was derived in university and National Science Foundation test reports and an actual earthquake, with the assistance of the inventor. The correlation of this data will allow the capable engineer to empirically select the proper core size and spacing for out-of-plane flexural loading or in-plane shear loading and other design details, as local government codes require.
Confirmation of the specialized Center-Core method as embodied in the earlier patent was established in the responses of the Center-Core retrofitted walls of six buildings within 12 to 20 miles of the earthquake epicenter in Northridge, Los Angeles, Calif., Jan. 17, 1994. This was a Richter 7 level earthquake. None of these Center-Cored buildings sustained even structural cracking in Center-Cored areas, while buildings around them cracked badly and structural failures with cracking and even partial collapses were common among masonry buildings in the same area. Many of the buildings around those with Center Core had received some strengthening measures, but without any type of wall strengthening.
The Center Core method applies to all masonry materials, but it is optimized more for the softer materials which are more common, worldwide, such as brick, soft sandstone and limestone, adobe, terra cotta and the like. It is less optimal, but still substantially preferable in most under-reinforced harder materials such as concrete, concrete block, or rock, including granite and basalt building materials. It has been applied in all such buildings; over 80 buildings have successfully received the method. Over 50 of these buildings were retrofitted by this inventor team with no quality control problems, whatsoever. Most of the remainder were almost certainly by U.S. Pat. No. 5,497,841 patent infringers. A few were by concrete wet drilling companies who had many problems in schedule delays, cost overruns and job failures.
The method also allows cutting of steel, including reinforcement, pipes, framing, hangers, lintels and the like, included in masonry structures and often not noted in original or present building plans, specifications and drawings.
In harder materials, use of water or other liquids in a mist as a coolant, or as coolant foams are often more efficient because of the superior cooling properties of these media, especially with the use of diamond bits. If possible, the water or foam is injected to just humidify and cool the air, but allow it to dry and keep the cuttings from caking after passing through the hot bit assembly.
The method of the basic patent in the air extraction of cuttings is employed insofar as possible in much the same way as with softer materials. Bits for harder materials usually have diamond cutting elements, while softer materials most often may be drilled with carbide elements. In all structural core-drilling applications it is highly desirable, and most often mandatory, to avoid employing water under high pressure to prevent mortar damage, masonry unit loosening and blowout, and water stains in exteriors and interiors. However, a limited use of coolants, usually water, in the Center Core air extraction method of the former patent in harder materials, as a mist or vapor in the air, or foam, can be advantageous.
The improvements and innovations herein patented are designed to illustrate and characterize, but not exhaustively record all usable configurations of the better novel hardware methods and system solutions for structural core drilling and resin grouting. The hardware applicability is primarily addressed to historically important structures in a world-wide employment of the methods patented in this and the previous method U.S. Pat. No. 5,497,841. The Center Core method is herein optimized further with novel innovations for expanded use.
The historical structures may be designed with enough cores to prevent structural cracking. However, all masonry buildings in seismically hazardous areas should use the method. For adequate public safety, the less historically or architecturally significant buildings can economically be retrofitted with fewer cores just to prevent building collapse. Center Core, applied in optimal ways, as in this patent, therefore may be widely used to save the lives being lost to earthquakes from failures of any masonry material, even in adobe or small earthen block structures. It applies cost-effectively to nearly all under-reinforced masonry, (URM), structures, constructed around the world.
The present patent also is addressed to the physical specifications for resinous grouting of the cores in optimal ways in all types of masonry. These procedures and materials also include quality control provisions, ensuring that cores will completely perform their functions. The entire Air Extraction Center-Core method or process is centered around the capability and capacity of the air extraction system which cools the bits and extracts the core-drilled cuttings. The complete method also is keyed to the strong, low viscosity resin-grouting system. Most importantly, integrated design of the entire system and employment procedures must be accomplished for optimally cost-effective operations.
Single-pipe Core Catcher Subsystem. As an example of the previously patented method, the inventors have inherently included an off-the-shelf hardware method termed the core-catcher subsystem, also called the core-lifter subsystem, FIG. 2. Various manufacturers have provided spring-loaded devices 60 to remove the inner portion of the core in solid, unpulverized form via a set of spring devices which catch and grasp pieces of the core at the bottom end and allow the operator to lift the entire column of the solid cored material with the drill string as it is withdrawn from the core. The spring-loaded devices are designed to allow the drill string always to be forced downward to cut more core, but snap into the solid-cored material, most often at a break point or mortar joint in the masonry core, to catch the material for withdrawal. Various techniques are used to break the solid core, if necessary.
The advantages of the core-catcher are that it can be employed to reduce the amount of material pulverized or ground up by the core drill 61, FIG. 2, and therefore it reduces the torque required for turning the drill column. It also reduces the amount of material that must be handled in dust and particles by the air stream and vacuum system, FIG. 1, thereby reducing the demand on the entire air extraction subsystem. The combination of all these advantages usually permits faster, less expensive core-drilling. However, to make room for the core catcher, wider kerf drill teeth FIG. 2, 59 must be employed. These wider kerf teeth remove a greater amount of material at the outer periphery of the core. The drill cuttings are then extracted outside of the single pipe 58, using the core-walls themselves as the second xe2x80x9cpipexe2x80x9d to extract the dust-laden air. At the wall entry point, a plenum catches the material and directs it via a tube to a large vacuum, and into a container as in the nominal U.S. Pat. No. 5,497,841 patent embodiment FIG. 1. The other features of the FIG. 2 core-catcher variation of the FIG. 1 patent, 50-57, are also included in the present patent, discussed below.
A wide kerf bit disadvantage is that the drill column is free to wander more. As the column becomes longer in deeper drilling, the torque required is greater and may tend to twist the column and cause it to wander off-center. Hard materials and voids encountered in the masonry also cause drill misalignment. Greater precision is required in the threaded ends of the pipe sections. To help resist torque wander and misalignment, off-the-shelf xe2x80x9creamerxe2x80x9d sections 56, used in geological applications to ream cores to larger size, may be adapted for use as bearing sections for the drill column. With the stiffness of the off-the-shelf drill pipe and deeper cores, reamers have often been required for accurate, controlled drilling. The reamer sections must have open spaces or spokes to allow the dirt-laden air to pass through them in the FIG. 2 prior art system.
The single-pipe, with double passage, using the core walls, and sometimes with an auxilliary plastic pipe to route the cuttings upward, is covered adequately under the method U.S. Pat. No. 5,497,841. An additional patent was not considered essential to illustrate variations of hardware used to carry out the method in this manner. However, in the present double-piped, triple passage patent, off-the-shelf hardware is not available to adapt to the method and, also, novel new hardware innovations are required to facilitate the new system features discussed below. Almost all components of the system must be redesigned for optimal drilling performance and increased capability. The key design details will be discussed below, though small innovations are also needed.
Limitations Of The Earlier System Configurations And Need For The Present Patent Innovations. The characteristic hardware configuration of the U.S. Pat. No. 5,497,841 patent, the full-core pulverizer as shown by the tri-cone example, is optimal only in a limited number of cases. While it would accomplish the core-drilling adequately in brick masonry walls up to 35 ft in depth or more, it was inherently less accurate than partial pulverization alternatives offered in the core-catcher approach. The core-catcher also drilled at a faster rate and was less costly in drill-bit wear and replacement. When 6 inch diameter cores were drilled, the tri-cone bit or any full pulverization bit became limited by the air extraction system in drilling rate and dust control because of the volume flow of dust-laden air required to achieve cost-effective drilling rate performance. The amount of dust became difficult to handle.
To meet the more demanding structural strengthening needs, the traditional construction design alternatives tend to be selected. These conventional methods include cementious gunite or shotcrete, poured-in-place panels or buttresses for wall-strengthening, or steel-framing to attach steel to existing masonry structure. These alternatives have been undesirable in historical retrofit projects where they would alter the architecture, but they could sometimes be selected for other buildings where historical preservation was not a significant factor. Only rarely were the alternative methods less expensive, but they are the traditional methods and would sometimes be substituted for the more cost-effective and architecture-preserving Center Core methods by conservative engineering firms.
While substantially more efficacious and cost-effective in most masonry structures, the Center Core method must be promoted to engineers. Full optimization of the equipment and procedures has been required to compete well with the traditional, less effective, less desirable structural retrofit methods. The ability to use the method efficiently in a large variety of structures was essential to its acceptance as a preferred retrofit method.
Another factor discouraging use of the complete pulverization system is the greater torque required to turn the drill column, especially at greater core diameters, limiting depth and rate of drilling.
Drilling rates directly determine cost of the drilling and low rates may even prohibit use of the method in less valuable structures. In addition, the pulverizer could not often pulverize steel, encountered frequently and unexpectedly in many Center Core projects. The steel could often be cut with the core cutting bit but could not be removed readily enough because it requires withdrawing the drill column. This xe2x80x9ctripping outxe2x80x9d to install and use steel cutters, then again to remove the steel, is a serious delay and cost factor in many core-drilling jobs.
These limitations of the full pulverizing hardware approach to dry core drilling were improved with the core-catcher approach to the method of the previous patent. Core catchers and reamer sections were available off the shelf and were adapted to the system for improvements in equipment cost, torque reduction, drilling rate, depth of cores to be accommodated, handling and column weight, a significant problem especially in greater diameters and lengths, and steel encounters.
The complexity of the plastic pipe riding on the drill body assembly was an additional complication and labor generator in the total pulverization system of the previous patent.
The previously patented system in the core-catcher variant also has other limitations. It is still difficult to adequately control the volume rate of dust generated from otherwise satisfactory drilling rates. With the core-catcher, the wide kerf bit is also not a good steel cutter, especially with the less costly carbide bit teeth. If the steel cannot be cut with the bit in use, an extra trip out and in to change the bit is added to the trip out and in to remove the steel from the bit.
The reamer sections usually required with the core-catcher are a small added labor factor. Even with them, it is still difficult to achieve desired accuracy. However, with care and increased drilling time, accuracy can be as good as one-tenth degree, about one inch in 50 ft of depth for cores to 30 or 40 ft of Depth. Core depths approaching 100 ft require excessively slow drilling rates, measured in lineal inches per minute, and add significantly to cost per lineal foot. Greater depths result in reduced accuracy and increased cost per lineal foot of drilling. The drilling is labor intensive and labor cost is therefore by far the greatest cost factor.
The U.S. Pat. No. 5,497,841 patent of FIGS. 1 and 2 thus encompassed the various means of employing a single pipe or shaft and auxilliary-piped, double-annulus core drilling systems. The systems were partially assembled from drilling hardware developed for, and utilized in geological or well-drilling applications; however, they were adapted as novel departures and modified from the configurations used in previous applications, with some fabrication of components specifically for the Center Core application.
The present invention could not be considered a further characterization of the U.S. Pat. No. 5,497,841 method or process system hardware. Hardware innovations of this patent are a substantial departure from adaptation of hardware used in geological, mining or well drilling operations. The present new designs have even greater specificity to the masonry building retrofit field and will significantly improve the hardware employed in present structural retrofit operations. There are many design details in the new designs which could only be envisioned from the experience with the previously patented systems. However, most important in these innovations is the proposed adaptation of aerospace fabrication methods, a departure from previous core-drilling hardware fabrication.
The above discussed limitations of the pulverizer and single-piped core-catcher approach are not totally prohibitive and will suffice in drilling rate performance for the softer masonry, lesser core depths, lesser core diameters, lesser accuracy requirements and infrequently encountered steel or other hard materials embedded in the structure. However, successful, but limited application of the FIGS. 1 and 2 pulverizer and core catcher systems has led to a realistic need for extended, less limiting hardware characteristics. The alternative system which is less limiting in these respects is that of the integral xe2x80x9cDouble-Piped, Triple-Passage Systemxe2x80x9d of this patent.
The pulverizing tri-cone or other pulverizer of the entire core was shown with a plastic pipe connected around the drill shaft riding on the drill body in U.S. Pat. No. 5,497,841, FIG. 1. The drill shaft had a hole through it""s length wherein the high pressure air was introduced to cool the bit assembly and entrain the drilling dust. But the entire core was pressurized at the relatively high pressure needed to move all of the material of the core upward with enough energy and far enough to be withdrawn by the vacuum at the drill entry point, FIG. 1. The speed of drilling, in lineal inches per minute, often became extraction-limited.
The pressure and energy to move the cuttings back up to the wall-entry point was substantially reduced by the obstruction and friction caused by the need to pass the air through the pulverizing inner bit. There was a great deal of leakage to atmosphere with higher core diameters and drilling rates. The plenum at the top, (or entry point if not drilling vertically), could be a source of air pollution which could coat all areas around the core with dust, if the vacuum plenum design is not carefully worked out and vacuum is not strictly maintained.
The full double-piped drilling system was always a possible solution to gain greater capability, including more depth, higher drilling rates and greater accuracy. But, it was initially rejected because of its somewhat greater complexity, cost and weight. As the pulverizer and single-pipe core-catcher were used in some fifty California, South Carolina and Utah projects, the limitations as to depth, drilling rate and accuracy, steel cutting, etc, were more and more obvious.
Finally, with the use of aerospace composite fabrication technology, the presently-proposed, alternative double-concentric column, triple-passage configured system was considered both practical and essential. The new technology permits a system design that deals with complexity, cost and weight adequately. The double-pipe drill system permits much greater depth, accuracy, drilling rates and reduced costs of drilling at reasonable hardware costs. The resulting design approach is the subject of this patent.